dns

client/dns.go

@@ -1,9 +1,12 @@
 package client
 
 import (
+	"context"
+	"errors"
 	"net"
 	"strconv"
 	"strings"
+	"time"
 )
 
 func LookupMinecraftSRV(host string, port uint16) (hostRet string, portRet uint16) {
@@ -22,19 +25,76 @@ func LookupMinecraftSRV(host string, port uint16) (hostRet string, portRet uint1
 	return
 }
 
-func DoDNS(in string) (out string, err error) { // Bad code should match minecraft
+type DNSCheckFunc func(addr string) error
+
+// DoDns resolves a DNS name to an IP address
+// It should resolve a minecraft compatible address into something net.Dial
+func DoDns(in string) (out string, err error) {
+	return DoDNSChecked(in, nil)
+}
+
+// DoDNSChecked resolves a DNS name to an IP address
+// It should resolve a minecraft compatible address into something net.Dial
+// It also optionally accepts a function to "check" the address
+func DoDNSChecked(in string, f DNSCheckFunc) (out string, err error) { // Bad code should match minecraft
 	// https://mcsrc.dev/1/26.1-pre-1/net/minecraft/client/multiplayer/resolver/ServerAddress#L34
-	host, port, _ := net.SplitHostPort(in)
+	host, port, err := net.SplitHostPort(in)
-	var portN uint16 = 25565
+	if err != nil {
-	if port != "" {
+		var addrErr *net.AddrError
-		var porti int
+		if errors.As(err, &addrErr) && addrErr.Err == "missing port in address" {
-		porti, err = strconv.Atoi(port)
+			err = nil
-		if err != nil {
+			host = in
+			port = "25565"
+		} else {
 			return
 		}
-		portN = uint16(porti)
 	}
-	host, portN = LookupMinecraftSRV(host, portN)
+	porti, err := strconv.Atoi(port)
-	out = net.JoinHostPort(host, strconv.Itoa(int(portN)))
+	if err != nil {
+		return
+	}
+	if f == nil {
+		f = func(addr string) error { return nil }
+	}
+
+	err = f(host)
+	if err != nil {
+		return
+	}
+	portN := uint16(porti)
+	outIP, err := net.ResolveIPAddr("ip", host)
+	if err != nil {
+		return
+	}
+	err = f(outIP.String())
+	if err != nil {
+		return
+	}
+	out = outIP.String() + ":" + port
+	if portN != 25565 {
+
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second) // otherwise this takes 10+ seconds
+	defer cancel()
+
+	r := &net.Resolver{}
+
+	_, srvs, _ := r.LookupSRV(ctx, "minecraft", "tcp", host)
+	if len(srvs) == 0 {
+
+		return
+	}
+	host = strings.TrimSuffix(srvs[0].Target, ".")
+	portN = srvs[0].Port
+	outIP, err = net.ResolveIPAddr("ip", host)
+	if err != nil {
+		return
+	}
+	err = f(outIP.String())
+	if err != nil {
+		return
+	}
+	out = outIP.String() + ":" + port
 	return
 }

client/dns_test.go

@@ -0,0 +1,21 @@
+package client
+
+import "testing"
+
+func TestDoDNS(t *testing.T) {
+	type Case struct {
+		Input  string
+		Output string
+	}
+	for _, c := range []Case{{"localhost", "127.0.0.1:25565"}, {"1f2d.net", "50.114.4.126:25565"}} {
+		t.Logf("Testing %s", c.Input)
+		out, err := DoDns(c.Input)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if out != c.Output {
+			t.Errorf("Expected %s, got %s", c.Output, out)
+		}
+	}
+}